Gin Admin theme - submit button issue

Ah I just realized I am using Cancel → button module. Once I disable it - it works as expected. So it is caused by this module. However once I disable ECA model it also works, so looks like ECA and Entity Form Cancel Button are not compatible in this case.

So not sure if anyone can help - and determine why ECA Entity Form Build Entity task has such "weird" impact.

It's actually not only the cancel button module and ECA, there is also Gin in the game which does a lot of magic to expose action buttons in the top-right corner of the sticky area. And even that will soon change a lot, as in Drupal core there will be the new navigation module and the toolbar module being removed. By then, Gin will no longer have to handle the sticky action buttons, and that'll change this whole behaviour too.

That said, I'm not sure if it's worth trying to figure out which component would have to be adjusted, could be all 3, actually.

Thank you for your information.

I have installed switch page theme → module for a temporary solution of my specific content type as it works fine with claro theme.

Yeah, neither Claro nor Drupal core without the upcoming navigation changes have the sticky action button behaviour. But that will become the default, or probably even the defacto behaviour without being able to disable that. So, modules that have a conflict with that should find ways around that rather sooner than later. Marking this as "Works as designed" as ECA is unlikely to be the one that needs a conflict between an admin theme and an altered action button.